1. Field of the Invention
The present invention relates to a light emitting device and a lighting apparatus using the same.
2. Description of the Related Art
In a field of general illumination, a solid-state illumination, specifically, a white light illumination using a semiconductor light emitting diode has attracted a lot of attention and thus researches and developments have been widely vigorously performed on the lighting apparatus.
In addition, such a white light emitting diode lamp has already acquired a luminous efficacy comparable or superior to that of an incandescent lamp, even though the diode lamp is still in the process of development. In the near future, the white light emitting diode lamp is thought to become widely used as energy-saving illumination equipment.
On top of that, the white light emitting diode lamp has another advantage of being free of substances that impose a heavy burden on the environment such as mercury or the like. Moreover, the diode lamp has so small a size that it is quite often used as a backlight source of a liquid crystal display apparatus or the like and built-in in a cellular phone or the like.
The above white light emitting diode lamp utilizes a white light emitting diode composed of a light emitting diode chip that emits a short wavelength light such as blue or the like and a phosphor that is excited by absorbing part or all of the light emitted from the light emitting diode chip and emits a longer wavelength light such as yellow or the like.
As an example of such a diode, there is cited a white light emitting diode composed of a compound semiconductor blue light emitting diode chip and a cerium-activated Yttrium Aluminium Garnet (YAG) phosphor that absorbs blue light and emits yellow light, which is a complementary color of blue (Refer to Japanese Patent Publications No. 2900928 and 2927279 and, “Development of High-bright and Pure-white LED Lamps”, K. Bando, K. Sakano, Y. Noguchi and Y. Shimizu, J. Light & Vis. Env. Vol. 22, No. 1 (1998), pp. 2-5).
In addition, a red phosphor may be added in order to compensate a low red component in the spectrum. Specifically, (Sr1-x-y-zBaxCay)2Si5N8:Euz2+, SrS:Eu, CaS:Eu, or (CaxSr1-x)S:Eu2+ as a red phosphor is added to a white light emitting diode composed of a blue light emitting diode chip and a cerium-activated YAG phosphor (Refer to Japanese Patent Application Laid-open Publications Nos. 2003-273409 and 2003-321675, and “Red-Enhanced White-Light-Emitting Diode Using a New Phosphor”, M. Yamada, T. Naitou, K. Izuno, H. Tamaki, Y. Murazaki, M. Kameshima and T. Mukai, Jpn. J. Appl. Phys. Vol. 42 (2003) pp. L20-L23).
Alternatively, there is another white light emitting diode that is realized with a blue light emitting diode chip, a first phosphor that emits green light upon excitation by blue light, and a second phosphor that emits red light upon excitation by blue light (Refer to Japanese Patent Application Laid-open Publication No. H10-163535).
Moreover, there is yet another white light emitting diode using SrGa2S4:Eu 2+ as a phosphor that emits green light upon excitation by blue light and SrS:Eu2+ as a phosphor that emits red light upon excitation by blue light (Refer to “Performance, Thermal, Cost & Reliability challenges for Solid State Lighting”, Paul S. Martin, OIDA Conference, May 30, 2002, for example).
Furthermore, an oxynitride phosphor and a nitride phosphor have now been subject to active researches, an example of which is a europium-activated Ca-alpha-SiAlON phosphor (Refer to Japanese Patent Application Laid-open Publication No. 2002-363554, for example). This phosphor emits yellow light when excited by blue light, and thus is preferable as a wavelength conversion material for use in a white light emitting diode.